1. Field of the Invention
The present invention relates to a method for fire-proofing a composite slab using a wire rope, and more particularly, to a method for fire-proofing a composite slab constructed of beams installed between columns, a deck plate installed between the beams and slab concrete poured on the beams and the deck plate, which allows a load transferred from the deck plate to be transferred to an upper portion of the beam via the wire rope to enhance a fire-proofing performance of the composite slab.
2. Discussion of Related Art
In general, a deck plate in the field of construction materials refers to a slab material manufactured by machining a metal plate such as galvanized sheet iron, and this deck plate is employed instead of a form and is not dismantled after pouring concrete to form a structure when a slab (also called a “floor slab”) of a building structure is constructed.
If the deck plate is employed to construct the slab, there is no need to utilize a form (formboard) for the slab concrete, and time and cost required for performing preparatory work such as construction of a form can be saved. Also, since the slab construction is performed by continuously placing and fixing the deck plates having a unit length on the beam, the construction can be easily carried out. In addition, the deck plates mass-produced in a factory are utilized so that is it possible to secure a quality higher than a certain level.
Recently, using the above deck plate for constructing the slab is a growing trend in the field of construction.
FIG. 1a shows an example method for manufacturing such deck plate.
In other words, thin plate-shaped materials for a slab formed into various bending panels as shown in FIG. 1 are mainly utilized in a long-span deck plate.
FIG. 1b shows an example of a double deck formed in the form of the above bending panel and installed on a beam.
In other words, from FIG. 1b, it can be seen that a deck plate 20 is installed such that an end portion of the deck plate 20 is supported by a lower flange 12 of a beam 10.
At this time, it can be seen that one end portion of each of the plurality of deck plates is supported by the beam 10. Thus, a reinforcing steel beam having a larger width is utilized to manufacture the lower flange 12 of the beam so as to easily support an end portion of the deck plate.
As shown in FIG. 1c, due to the above, since a section of the beam 10 is designed such that a weight of the beam, a weight of the deck plate and a weight of a slab concrete 50 in which a reinforcing bar 52 is arranged can be supported, a section of the beam can be variously obtained.
Furthermore, if fire breaks out in a building constructed with the slab concrete 50, the concrete can be explosively fractured by flames, and if the concrete is explosively fractured, structural members surrounding the concrete, for example, the beam 10, are influenced by the flames.
Thus, once a stiffness of the beam 10 supporting a weight of the deck plate and the slab concrete 50 in which the reinforcing bar 52 is arranged is lowered by the flames, the building will indubitably collapse.
In order to prevent a stiffness of the beam formed of steel material from being lowered by the flames, a construction method for covering the beam and the deck plate with a spray coating material (indicated by the grey part) for thermal insulation has been introduced as shown in FIG. 1d. 
In the fire-proofing method utilizing the above spray coating material for thermal insulation, however, a problem of securing a quality in a thickness of the spray coating layer can occur, and thus strict quality control is required (lowering of workability and constructibility). As a result, a construction period is increased and this causes an increase of construction cost.
FIG. 1e shows a construction method for preventing a lowering of stiffness of the slab caused by an increase of temperature without utilizing the spray coating material. In this method, a fire-proofing board (indicated by the violet part) is attached to a region including a central portion of the deck plate in the composite slab for thermal insulation in the event of fire.
However, if an adhesion property of the fire-proofing board deteriorates, a stiffness of the beam and the like which are directly exposed to the flames may be rapidly lowered. Also, an installation of the fire-proofing board causes an additional process and an increase of construction cost, and the construction cost and the construction period are increased due to expensive materials (the fire-proofing board, a frame for installing the fire-proofing board and the like).
FIG. 1f shows a deflection controlling method for preventing deflection of a central portion of the beam 10, which is one of conventional fire-proofing methods.
In the conventional composite slab, in other words, since deflection of the central portion of the beam is increased in the event of fire in proportion to a distance between the beams which are exclusively responsible for the load, casualties are caused by a collapse of the slab.
Accordingly, to control deflection of the central portion of the beam, a technique of controlling deflection of a central portion through tendons (shown as three rods) utilized for introducing pre-stress to a web of the beam has been applied.
In other words, in order to complement a reduction of stiffness caused by the flames, the above method does not include forming the spray coating layer or attaching a fire-proofing board to the beam 10, but rather introducing the pre-stress to the beam.
For the beam having a relatively high stiffness, it is possible to control deflection of the central portion through the tendons (pre-stressing strands, steel bars and the like). However, there is a limit to which the above pre-stressing method can be applied to the deck plate.
This is because, since the deck plate is a thin plate-shaped material for the slab and is frequently manufactured from a bending panel, if a strong pre-stress of the tendon is introduced to the deck plate, it is not easy to anticipate the structural performance due to a shape change of the deck plate.
Also, if the tendon is directly installed on the deck plate, workability and constructibility necessarily become less efficient. This is because since a steel bar (pre-stressing strand) is utilized as the tendon employed for securing the fire-proofing performance, the efficiency in machining and installation of the above material is extremely low.